Record carriers of this type have been known for quite some time. In the production of record carriers that are vapor-deposited with aluminum or coated therewith, it is necessary for various reasons, especially in view of the necessary dullness, the copying characteristics after printing, and the correct burnishing during printing, that the surface show a certain roughness. This is because fillers in the lacquer layer beneath the aluminum layer more or less protrude from the surface. The dullness increases with the amount of admixed fillers, since the light diffusion increases through the closely packed arrangement of the pigment bodies, i.e. the density of peaks per surface unit. However, there also increases the sensitivity to abrasion and scratching traces, as during printing the electrodes merely slide over the peaks of the pigment grains, and tear the aluminum layer there. With an increasing filler proportion, the sharpness of the protruding pigment grain contours increases, too, since the grains have scarcely any surrounding lacquer left. Furthermore, highly filled lacquers are always less stable and therefore show a chalking tendency.
There exist various methods of reducing the abrasion and scratching traces by means of the lacquer composition selected:
(a) Low pigment-content, high-gloss lacquers with soft pigments as e.g. carbon black or CaCO.sub.3 are used. Such record carriers have a high degree of brightness of 40% to 50%. As a calibrating standard a planar, polished black glass plate is used having a degree of brightness of 100%. With a degree of brightness of 40%, the copying characteristics are still rather poor. On the other hand, the electrode abrasion is low. The characteristics with respect to abrasion or scratching traces, however, can substantially be improved in that a gliding layer on the basis of a metallic soap in accordance with German patent application No. P 30 07 331, German patent application No. P 30 11 591 and, in particular, the metallic soap in accordance with German patent application No. P 30 32 223.7, is used to which 10 to 30% by weight of a multi-functional, aliphatic, saturated or unsaturated alcohol are admixed. A thus modified metallic soap is preferably applied to the aluminum layer surface by rubbing on, rubbing in and polishing.
(b) Very hard fillers (e.g. quartz powder) are used which cannot be destroyed by the print electrodes. The lacquers are highly filled, too, with the filler having merely to be firmly embedded in the lacquer to avoid chalking. These lacquers have a very low degree of brightness of up to 10% and have thus very positive copying characteristics. They can also show an extremely low amount of abrasion traces since the electrodes slide only on the peaks on the pigment grains but cannot destroy them. The only, but rather important, disadvantage of such a pigmenting is the extremely high electrode abrasion.
Here, too, the abrasion traces can be reduced by using metallic soaps, or modified metallic soaps in accordance with the above-mentioned German patent applications.
In all cases, however, a maximum adhesion of the aluminum layer over the entire surface is an essential condition for a low amount of abrasion or scratching traces.
Highly-filled lacquers with few abrasion traces should contain hard pigments since with soft pigments surface damage is too high, which in turn causes strong abrasion traces.
The quality of the polymer used for the lacquer is of course very important too, but even the hardest and toughest polymer, with a high filling with soft pigments will always show quite strong abrasion traces. This is due to the sharp surface contours of the protruding pigments, and to the destruction of the pigments by the electrodes, as well as to the high surface pressure by the electrodes caused by the form of the pigments.
Quite generally, it can be said that highly filled lacquers practically show an angular or acicular waviness of the surface, and that thus the necessary dullness or the necessary degree of brightness are easily achieved. For high copying characteristics, degrees of brightness of 20% to 25% are required. Experience has shown that a degree of brightness of less than 20% involves a too high graying of the aluminum layer, which can be explained by the increased light absorption at the sharp edges. With a degree of brightness of 10% to 12% the paper is visibly gray.
With the low pigment content-lacquers the situation is different, i.e. the electrode slides only over a few pigment grains, which furthermore are coated with a rather thick lacquer layer, and thus protected. The surface pressure of the electrodes is high, too, but the contours of the protruding pigments are of a soft waviness. Thus, the polymer is exposed to very high strain at the few points of contact. Since this waviness is of a very low frequency the dullness is low, too.
Therefore, the hitherto available lacquers do not permit a perfect solution for the problem of abrasion traces, even when specifically modified metallic soaps are used.
The object of the invention can thus be defined as follows. A surface of the lacquer layer and consequently of its covering and very thin aluminum layer is to be provided, with the following properties:
1. a high frequency of the waviness,
2. a soft waviness,
3. a high mechanic strength and toughness through thick lacquer layers on the pigment grains,
4. a high dullness,
5. a low graying,
6. a low electrode abrasion, and
7. a homogeneous adhesion of the aluminum layer to the lacquer layer.
Preferably, the following characteristics are to be achieved, e.g.
8. a low surface pressure of the electrodes, and
9. a low strain on the lacquer layer.